1.Grease deep 25cm round cake pan, line base with baking paper. Using both packets, prepare cake mix according to directions, pour into prepared pan. Bake in moderate oven about 1 hour. Stand cake in pan for 5 minutes, turn onto wire rack to cool.
2.Tint melted chocolate with blue colouring, add some corn syrup, stir until mixture thickens and becomes slightly grainy. Cover, stand at room temperature about 1 hour or until mixture is firm
3.Using picture as a guide, cut out the marble bag. Place cake, base-side up, on the board.
4.Using a sharp knife, slightly trim top of cake at an angle towards “opening” of the marble bag. Brush top and sides of cakes evenly with warm jam.
5.On a surface dusted with icing sugar, knead blue chocolate mixture until smooth and soft. Roll out on a sheet of baking paper until large enough to cover top and side of cake. Carefully place chocolate on cake, press firmly around side of cake, trim around edge (except for the bag’s opening), reserve any leftover chocolate mixture.
6.Gently ease the chocolate mixture around the bag’s opening into decorative folds. Re-roll reserved excess chocolate mixture, place in folds around opening to make a double layer, trim to neaten edges. Roll a sausage shape about 10cm long from chocolate trimmings, press over joins of decorative folds.
7.Using a skewer or a toothpick, pierce holes about 1.5cm apart on the bag’s opening, press short pieces of licorice into holes to look like stitched-in drawstring. Bend two 60cm pieces of licorice in half and attach to side of opening to resemble the pulls on drawstrings. Place the gum balls in position and pipe a message on the bag with decorating gel.